1. Field of the Invention
This invention relates to a method of forming a pattern and an insulating film for use in the manufacture of an electronic element such as a semiconductor device or a liquid crystal display device, and to a silicone polymer composition for forming the pattern and the insulating film.
2. Description of the Related Art
A fine working technique using a photoetching is extensively utilized in the manufacture of electronic parts of various kinds including a semiconductor element and an integrated circuit. For example, in the manufacture of electronic parts, a resist film is first formed through a spin coating on a monocrystalline silicon wafer and then a mask having a desired pattern is superimposed on the resist film. Then, a light exposure, a development and a rinsing treatment are successively performed through the mask to form a pattern of the resist film. With this resist film pattern being formed on the wafer, an etching is performed to form desired lines and openings on the wafer. The degree of precision of this fine working technique in an electronic product is largely dependent on the performances of a resist material to be used, i.e. the resolution of the resist material on a substrate, the accuracy of photosensitivity of the resist material, the adhesion of the resist material to a substrate and the etching resistance of the resist material.
Recently, there has been an increasing expectation to the employment of polysilane as a resist material. For example, Japanese Patent Unexamined Publication No. S60-228542 discloses a technique of forming a positive pattern by making use of polysilane. The resist of this kind comprising a silicon-containing compound such as polysilane is featured in that a SiO.sub.2 -like film is formed on the surface of the resist by an oxygen reactive ion etching (oxygen RIE) after the formation of a resist pattern, thereby making it possible to obtain a resist pattern which is excellent in oxygen RIE resistance.
According to this known method, actinic radiation is irradiated onto polysilane to generate a volatile photo-depolymerized product, which is then evaporated, thus forming a pattern. However, in the method making use of such a dry phenomenon as explained above, it is very difficult to form a fine pattern in high precision. Moreover, the conventional method of forming a pattern by making use of polysilane is still defective in the respect of realizing a sufficient sensitivity of the polysilane.
Meanwhile, in the manufacture of a semiconductor device or a liquid crystal display device, it is required to form an insulating layer on the surface of a liquid crystal display device or on the surface of interconnecting wirings for securing an insulation of these surface from other element regions. In the formation of an insulation film for covering an interconnecting wiring, the following method has been conventionally adopted.
(1) A method of depositing a silicon compound by way of a CVD method.
(2) A method wherein a solution comprising an alkoxy-containing polysiloxane formed of polysiloxane whose side chain is substituted by alkoxy group is coated on a substrate, and then the alkoxy group on the side chain is dissociated with water to generate SiOH, which is then condensed, thus forming a crosslinking Si--O--Si bond.
(3) A method wherein an organosilica sol of an alkoxy-substituted silane such as tetraethoxy silane or of alkoxy-containing siloxane of low molecular weight is coated on a substrate, the resultant coated layer being subsequently thermally dried.
(4) A method wherein a solution comprising a polysilane whose side chain is substituted by alkoxy group is coated on a substrate, and then the alkoxy group on the side chain is dissociated with water to generate SiOH, which is then condensed and at the same time the backbone chain of the polysilane is photo-oxidized, thus forming a crosslinking Si--O--Si bond.
(5) A method wherein a solution comprising a polymer constituted by a two-dimensionally extended polysilane is coated on a substrate, and the resultant coated polymer layer is photo-oxidized and thermally dried, thus forming a crosslinking Si--O--Si bond.
However, even with these methods (1) to (5), it is still difficult to obtain an insulating film of good quality, which is excellent in surface flatness and free from cracking associated with the volume shrinkage.
For example, the insulating film to be formed by way of a CVD method according to the aforementioned method (1) is defective in surface flatness. Meanwhile, it may be possible, with the employment of the aforementioned methods (2) to (5), to easily obtain an insulating film of desired film thickness, which is excellent in surface flatness. However, the aforementioned method (2) is accompanied with a problem that the large alkoxy group is eliminated in the process of cross-linking during the thermal drying step, so that a prominent volume shrinkage of the polymer may be resulted. Furthermore, this method is also accompanied with a problem that the polymer may be gradually hydrolyzed during the storage thereof, thus indicating the poor storage stability thereof.
On the other hand, the aforementioned method (3) is also accompanied with a problem that the large alkoxy group is eliminated in the process of cross-linking during the thermal drying step, so that a prominent volume shrinkage of the polymer may be resulted. In particular, since the cross-linking is effected from a low molecular weight material, cracks resulting from the volume shrinkage may be generated in the insulating film to be formed. Furthermore, since the organosilica sol may be gradually hydrolyzed during the storage thereof, it may give rise to the problem of poor storage stability. The aforementioned methods (4) and (5) are also accompanied with problems that the prepolymer to be employed therein tends to be easily gelated, thus making it difficult to form a coated layer, and that the storage stability the prepolymer is poor.
It is some times required that an insulating film formed on an interconnecting wiring is patterned to form a contact hole. However, it is very difficult to perform such a patterning on the insulating film to be formed according to the aforementioned methods (1) to (5). Namely, a resist pattern is first deposited on the insulating film, and then the etching of the insulating film is performed using the resist pattern as an etching mask, the resist pattern being required to be peeled away subsequently. Thus, since the manufacturing process becomes very complicated according to these methods as indicated above, the insulating film pattern can not be obtained in an inexpensive manner.
In view of this, there has been proposed a technique to simplify the process of forming an insulating film pattern, wherein the photo-sensitivity of polysilane is made use of. According to this technique, after polysilane is patterned, the resultant pattern is heated to turn it into an insulating material. More specifically, since polysilane is featured in that the molecular weight thereof can be decreased when it is exposed to the irradiation of ultraviolet rays, a pattern of polysilane film can be formed by the steps of selectively exposing the polysilane film to the irradiation of ultraviolet rays, and then dissolving the irradiated portion of the polysilane film with the use of a polar solvent such as alcohol or ketone to develop the pattern of the polysilane film. Subsequently, after being further irradiated with ultraviolet rays if required, the resultant pattern is heat-dried to turn the polysilane into a siloxane, thereby obtaining an insulating film pattern.
However, since the pattern thus obtained is formed of a single-dimensional siloxane obtained by heat-drying polysilane, the pattern is defective in reliability in terms of heat resistance etc. if it is to be used as an insulating film. Moreover, the pattern obtained in this manner is poor in adhesion to a substrate.
Recently, it is reported that when polysilane is irradiated with ultraviolet rays and then immersed in a solution of a dyestuff, the ultraviolet ray-irradiated portion, or photo-oxidized portion of the polysilane film can be selectively colored (Yokoyama et al, Chemistry Letters, 1563 to 1566, 1991). Therefore, a method of manufacturing a color filter making use of this phenomenon has been tried. For example, in Japanese Patent Unexamined Publication H5-88215, there is proposed a method of manufacturing a color filter wherein a film of polysilane represented by the following general formula (5) is deposited on a substrate, and then a sequence of steps comprising a selective irradiation of ultraviolet rays to the polysilane film and a dipping of the polysilane film in a dyestuff solution is repeated for each of three colors, i.e. R, G and B. ##STR2##
wherein R.sup.50, R.sup.51, R.sup.52 and R.sup.53 may be the same or different and are individually a substituted or non-substituted hydrocarbon group; m and n are respectively an integer.
Namely, according to this method of manufacturing a color filter, the step of developing a resist pattern is not required at all and the step of forming a film may be performed once for all. Therefore, the manufacturing process of color filter can be extremely simplified as compared with the ordinary method of using a negative resist film containing a color component. Furthermore, since the formation of film for three colors of R, G and B can be performed en bloc, a color filter of high precision having a flat color layer can be manufactured. However, the polysilane represented by the aforementioned general formula (5) is accompanied with the problems that the adsorption rate of a dyestuff onto an ultraviolet ray-irradiated portion is rather slow so that a long period of time is required for coloring the ultraviolet ray-irradiated portion, and that the durability and mechanical strength of the colored layer are insufficient for the actual use.
As explained above, even though the formation of patterns using polysilane as a resist material has long been tried up to date, it has been difficult with the employment of polysilane to form a fine pattern in high precision, and the sensitivity of the polysilane has been in most cases proved to be insufficient. Meanwhile, if the formation of pattern by way of an alkaline development is possible, the precision of pattern may be expected to be improved. However, polysilane is generally insoluble to an aqueous alkaline solution, so that it is impossible to form a pattern by way of an alkaline development.
On the other hand, with regard to an insulating film formed of polysilane, it is still failed to obtain an insulating film which is excellent in surface flatness and also in film quality, and at the same time the reliability of the insulating film in terms for example of adhesion onto a substrate is still unsatisfactory.
There has been also proposed to employ a specific kind of organic polysilane in place of the conventional negative resist film and to omit the developing step by selectively coloring an ultraviolet-irradiated portion of the organic polysilane. However, the method is also accompanied with the problems that it takes a long period of time for coloring the ultraviolet ray-irradiated portion, and that the durability and mechanical strength of the colored layer to be obtained are poor.